So far i've done everything i can think of to increase my mileage. It's gone down like crazy from 27 to 22. Other than a little bit wider tires i dont know what could cause it. Is it possible something like an oxygen sensor could be bad causing this problem without causing a CEL?

I'd get it checked just in case, fuel filter, spark plug's, clean off your filter if u have a cold air intake. :beer:

How you get it checked?

autozone, or look it up dsmtuner.com as alot of good answer as well

I've also heard that running slightly higher pressure in your tires adds to gas mileage. But nothing helps more than taking it easy with the right foot.

do you know if your running rich or lean?

dont feel bad, I went from 29 to 16 and dont know wtf happen either

^are you serious and you ahvent checked that out? its not that hard.

My buddy just put in one of those home made hydrogen fuel cells and he gets great mileage.

I'm building those as well.

If you haven't already try to find a fuel that doesn't have ethanol in it. My 4G went from averaging about 25 to averaging 14 at approx 30k miles. I checked everything that I could. Cleaned MAS, checked plugs, cleaned air filter, changed the clutch (it was slipping and after changing it my mileage went up to 16), and anything else I could come up with that could cause the problem. I had a friend tell me that shell doesn't put ethanol in their gas so I figured I would try it. After 2 tanks of gas my mileage went back up to about 22 - 23. I don't know what gas stations you have around your house but around here Luk Oil, Shell and Exxon don't put ethanol in their gas.

I dont think cali has ethanol anywhere. I always go to either shell or chevron, and no matter where i get gas mileage is about the same. I'm already running the tires higher pressure than what the door says to :P I do have 225/50/16 tires. But i dont think that is it. Also, it doesnt seem to matter much how i drive i still get between 21 and 24. I used to get 30 on the freeway @ 75mph. How do i determine if i'm running rich or lean?

lol air/fuel ratio guage will give you an idea, but if you want to know exactly how much fuel your using then maybe a wideband air/fuel ratio guage.....:)

A wideband is really the only option in determine AFR. A narrowband o2 and gauge will give you a readin, but it wont be anywhere near accurate enough to matter. Narrowband o2s and gauges are strictly for light shows.

Why dont you try those magnets around the fuel lines. Or the tornado things in the intake. :grin: JK The cheapest way to tell is to put your hand over your exhaust for a few seconds, and if it smells like you just took it out out of a gas can your rich.

check your plugs too, darker means your running rich and whiter means your lean.

I have been designing one of those for a while now and have a pretty good design. in the process of building it to test it out